Scores for 65 countries (or "economies") are now out from the OECD's Programme for International Student Assessment (PISA). How have scores in the U.S. changed since PISA got going in 2000? 

From the federal NCES explorer tool for PISA scores:

Scores were down slightly in 2012 versus 2009, but they had been higher in 2009 than in preceding years (when, unfortunately, not all three subjects had been tested). Overall, 2012 scores look about the same as 21st Century scores in general, with no consistent trends visible in any subject.

So, that's kind of boring. The reason I mention it is because PISA results usually lead to great wailing and gnashing of teeth about Decline, etc.

PISA tests are scored like SATs with 500 as the intended mean for wealthy OECD countries (it usually slips below that) and a standard deviation of 100. So a 400 is at the 16th percentile for the OECD and 600 at the 84th percentile.